1. Field of the Invention
The invention refers to a fuel injection nozzle for internal combustion engines, especially Diesel engines, comprising a spring-loaded valve needle and a displacer piston sliding with the needle along the same axis against the force of the valve needle spring, in which nozzle the displacer piston and the valve needle are connected with the fuel pressure chamber of an injection pump.
2. Description of the Prior Art
A device according to the above-mentioned type can be taken from DE-OS No. 34 09 924, for example. Providing a displacer piston, which is mounted parallel to the valve needle with regard to the admission of fuel, serves to divide the injection process into a pre-injection and a main injection. For this purpose the valve needle is first lifted against the force of the valve needle spring during a pressure build-up in the fuel pressure line, through which the injection process is initiated. Thereafter also the displacer piston is shifted against the force of the valve needle spring because of the increase of pressure in the pressure line, through which first the force acting on the valve needle spring is increased and second a short decrease of pressure occurs because of the opening displacing volume, which decrease leads to a short shutting of the valve needle. The continuously rising pressure lifts the valve needle once more against the force of the prestressed valve needle spring, thus beginning the main injection.
With the known devices of the initially mentioned type the displacer piston was arranged in a separate component, where this additional component was housed in a series of high-pressure-components being clamped with each other. The additional components resulted in an increase of the length of the nozzle construction and regarding an unfavourable ratio of the aperture cross-section of the piston relative to the guiding cross-section of the piston the pressure relieve taken place relatively slowly with the known devices, especially in the higher speed range. Providing a longer displacer piston would require greater dimensions and would additionally enlarge the inertia of the construction. To limit the height of construction a relatively small ratio of the guiding dameter relative to the guiding length of the displacer piston had to be observed, through which yet again quantities of overflow oil occured and the risk of a tilting and blocking of the displacer piston existed.
Especially when using a monobloc injection pump and nozzle the additional amount of height of construction represents a big disadvantage, the addition height resulting from such an intermediary part.